1. Technical Field
The present application relates to medical devices for the treatment of atelectasis/airway collapse (AAC).
2. Related Art
Physiologic breathing in healthy individuals is accomplished by maintaining a negative pressure field inside the pleural cavity. This negative pressure field is enhanced by the downward motion of the diaphragm and upward and outward motion of the rib cage resulting in inspiration. Relaxation of these muscles results in exhalation which is passive, requiring no energy. The apexes of the lungs having a greater negative pressure than inferior lobes due to gravity's effect on lungs.
Atelectasis/airway collapse (AAC) is a serious medical problem that occurs in a number of respiratory conditions caused by a wide range of etiologies. AAC often results in respiratory impairment and/or failure. In a typical case, a patient experiencing AAC is treated with intubation and mechanical ventilation using positive pressure.
During positive pressure ventilation of sedated or paralyzed patients, airflow into the lungs takes the path of least resistance. In this scenario, the healthy section of lung presents the path of least resistance as the collapsed and/or obstructed airway restricts airflow. This phenomena is problematic as the medical professional must carefully recruit the atelectatic or sick lung fields without overinflating and thereby damaging the healthy lung.
This problem is exacerbated by mechanical ventilation strategies, as recruitment usually involves increasing distending pressures either by increasing peak inspiratory pressures, or by delivering more volume. Both of these techniques increase the likelihood of barotrauma from over inflation of the healthier more compliant lung tissue.
To address these problems, negative pressure ventilators have been developed. For example, the earliest negative pressure ventilators developed at the turn of the 20th century relied on negative pressure via the “Iron Lung.” In such a system, a patient is placed into a large steel chamber that forms a sealed, air-tight compartment around the patient's entire body with just their head outside the iron long as pumps periodically decrease and increase the air pressure within the chamber to cause the lungs to fill with or expel air to mimic the physiological action of breathing. Modern equivalents such as the Hayek Chest Cuirass (provided by Hayek Medical of London, England, UK) employ the same principle using a chest cuirass that covers the chest and abdomen.
While these negative pressure ventilators provide certain benefits, they also pose problems of their own. For example, blood pooling in organs such as the liver can occur due to the negative pressure field applied over the abdomen. In addition, because these devices rely on the formation of an air tight seal around the affected lung, they inhibit access to the patient. As another example, these devices are difficult to set-up and keep on a patient, which can be critical in an emergency care situation.
Accordingly, a need has long existed for improved systems and methods for lung expansion.